DESCRIPTION (Investigator's Abstract): Near-ultraviolet light from sunlight is known to increase the risk of formation of human cortical cataracts. The mechanism of action of different wavelengths of near-UV radiation on the lens is unknown at present. The focus of this study is to quantitate the biological effectiveness of specific wavelengths of radiation between 297 and 400 nm on the lens and lens constituents. Action spectra for lens opacification by monochromatic wavelengths in UVB (297-320nm) and UVA (320-400 nm) will be determined under biologically meaningful conditions. Intact bovine and human lenses and homogenates will be used. Spectroscopic techniques and protein crosslinking will be used to assess the damage. Quantitative studies on the generation of specific reactive oxygen species will be done, to assess their role in photodamage at different wavelengths. Less than ten percent of UVB and 60 percent of UVA reaches the human lens epithelium in vivo. However, UVB and not UVA increased the risk of cortical cataract formation in a recent human epidemiological study. The biological effects of UVB and UVA radiation on lens epithelial cells are unknown at present. Quantitative action spectrum studies on the cell survival, synthesis of newly synthesized proteins and DNA damage in lens epithelial cells are planned in this study. These data will provide quantitative information on the biological effects of near-UV wavelengths on the epithelium. Normal human lenses of different ages (infant, young and old), and cataractous lens epithelia will be investigated to determine the mechanism of action of near-UV radiation of the human lens in vivo. The long-term objective of this proposal is to define a molecular mechanism for the changes in lens constituents and obtain a better understanding of the link between photodamage and human cataract formation.